In physics, static equilibrium exists when the forces (actions) on all components of a defined system are balanced with the reactions such that no component is undergoing an acceleration relative to the designated frame of reference.

Examples: A paperweight on a desk. If an inertial reference is chosen to be identical to the motion of the room, then the system of the desk and paperweight can be considered as in static equilibrium with respect to the floor. Small accelerations due to the background motion of Earth (see Coriolis effect, centripetal acceleration) are neglected by choosing this coordinate system for analysis of the system.

For related detailed analysis methods see engineering mechanics and statics.

See also: Dynamic equilibrium